The present invention relates to a spindle motor and a rotator device in which a rotor is fixed at a rotating shaft included in a liquid dynamic pressure bearing and a stator is fixed at a housing included in the liquid dynamic pressure bearing.
FIG. 4 is a sectional view showing the spindle motor disclosed in U.S. Pat. No. 5,487,608. In the spindle motor, a rotating shaft 1 included in a liquid dynamic pressure bearing is worked in one body with a rotor 2. A ring-shaped thrust bearing member 4 is put into a small diameter hollow portion 3a of a two stage hollow portion formed at lower face of a housing 3 in the housing included in dynamic pressure bearing portion through rotating shaft 1, and is fitted by force to the rotating shaft 1. An oil receiver is formed between the small diameter hollow portion 3a and the thrust bearing member 4. Forcing a presser ring 5 into a large diameter hollow portion 3b, lubricant oil is filled in the circumferential space of the rotating shaft 1. The thrust dynamic pressure bearing is formed at both sides of the thrust bearing member 4, and a radial dynamic pressure bearing is formed at circumferential face of the upper rotating shaft 1 rather than the thrust bearing. At high speed rotation, radial dynamic pressure generating grooves are formed so that net flow of lubricating oil orients in the direction of the thrust bearing, and thrust dynamic pressure generating grooves are formed so that net flow of lubricating oil orients in the radial direction. Therefore, lubricating oil does not leak when the motor rotates at high speed. A capillary seal comprising an oil receiver 6 is provided at the place where lubricant oil is exposed to air from the outside so that lubricating oil does not leak when the motor stops. The radial bearing and the thrust bearing are connected through communicating holes 9a, 9b, and 9c so as to allow the smooth flow of lubricant liquid.
However, in the above-mentioned spindle motor it is hard to form the radial dynamic generating groove because the rotor 2 and the rotating shaft are formed in one body. By forming the thrust bearing member 4 at the lower portion of the rotating shaft 1, both faces of the thrust bearing member 4 form the thrust dynamic pressure bearing, and upper side circumference face of the shaft rather than the thrust bearing member 4 of the rotating shaft 1 forms the radial dynamic pressure bearing. As connecting the radial bearing and the thrust bearing through communicating holes 9a, 9b, and 9c causes a failure in keeping highly accurate rotating balance, incline of the rotor toward the stator becomes large at starting and stopping of rotation. Therefore, contact occurs easily between members comprising the bearing, and there is a possibility of shortening production life and cause of half whirl phenomenon. The spindle motor can not be used for an HDD (Hard Disc Drive) in which deflection should be extremely small, for example, less than .+-.5 .mu.m at 7 to 8 mm from center of rotation of the rotor in axial direction, and less than .+-.2.5 .mu.m in the radial direction. It is hard to form the radial dynamic pressure generating groove at the rotating shaft 1 formed with the rotor 2 in one body, and it causes high cost. Moreover, connecting the radial bearing with the thrust bearing through the communicating holes 9a, 9b, and 9c causes high cost.
In another prior art method, there is a method of forming separately the rotor and the rotating shaft accurately and fitting and fixing them taking about 1 to 200 .mu.m space between them using adhesive and connecting shaft. By the method, the center of rotation of the rotating shaft and the rotor deflect, and their centers of rotation of are not parallel. Therefore, deflections of axial direction and radial direction in the above-mentioned spindle motor for HDD and the like can not be smaller than the required minimum value. Adhesive flowing in unnecessary areas causes more trouble.
Still in another prior art method, after forming separately the rotor and the rotating shaft with some degree of accuracy and assembling the spindle motor by pressing together lightly the rotor and the rotating shaft, working for increasing deflection is carried out in order to make deflection of axial direction of the rotor less than the designed value driving the rotor. By the method, it is possible that chip comes inside of the motor.
The present invention is intended to solve the above-mentioned problems, and an object thereof is to provide a spindle motor and a rotator device in which deflections of axial direction and radial direction are extremely small while the half whirl phenomenon does not occur and it is easy to produce.